Refrigeration Installation and Method for Operating a Refrigeration Installation

ABSTRACT

A refrigerating system comprises at least one refrigerating consumer provided with at least one evaporator, at least one supply line and at least one withdrawal line which enable the coolant or the coolant mixture to be supplied to and/or withdrawn from the refrigerating consumer(s). Expansion elements are associated with the evaporator(s). The expansion elements are embodied as modified expansion valves and/or as modified linear expansion machines or the by-pass lines are associated therewith, and a modified linear compressor or a traditional compressor, which comprises a by-pass line is associated with each refrigerating consumer. The modified expansion valve(S) and/or the modified linear expansion machine(s) and/or the modified linear compressor(s) have a working position which enables a through-flow without a considerable drop in pressure.

BACKGROUND (1) Field of the Invention

The invention relates to a refrigeration installation having at leastone refrigeration consumer, which includes at least one evaporator,having at least one feed line and at least one discharge line, via whichthe refrigerant or refrigerant mixture is fed to the refrigerationconsumer(s) and discharged from the refrigeration consumer(s),respectively, the evaporator(s) being assigned expansion members.

Furthermore, according to a first alternative, the invention relates toa method for operating a refrigeration installation in which therefrigeration compressor(s) is/are assigned modified expansion valvesand modified linear compressors.

According to a second alternative, the invention relates to a method foroperating a refrigeration installation, in which the conventionalexpansion valve(s) and the conventional compressor(s) of therefrigeration consumer(s) is/are assigned bypass lines.

In the text which follows, the term “modified expansion valves” is to beunderstood as meaning all expansion valves which, in addition to theprimary function of “expansion of a liquid”, have the secondary functionof “realization of a fluid connection”. The term “modified compressor”in the text which follows encompasses all compressors which, in additionto the primary function of “compression of a gas”, also allow thesecondary function of “realization of a fluid connection”.

The terms “conventional expansion valves” and “conventional compressors”in the text which follows are to be understood as meaning all knowndesigns of expansion valves and compressors which do not have theabove-mentioned secondary function.

Refrigeration installations of the generic type are used for example insupermarkets or hypermarkets, where they generally supply a multiplicityof refrigeration consumers, such as cold stores, refrigerator cabinetsand/or freezer cabinets. For this purpose, a one-component ormulticomponent refrigerant or refrigerant mixture circulates insidethem. A refrigeration installation of this type—as is known from DE-C 3928 430—has a liquefier, in which the pressurized refrigerant (mixture)is condensed by indirect heat exchange, preferably against outside air.

The liquid refrigerant (mixture) from the liquefier is fed to acollection vessel that is optionally to be provided. Within arefrigeration installation, there must always be enough refrigerant toensure that the evaporators of all the refrigeration consumers can befilled even during the maximum demand for refrigeration. However, sincewhen the demand for refrigeration is lower some evaporators are onlypartially filled or are even completely empty, the excess refrigerant(mixture), during these times, has to be collected in the collectionvessel provided for this purpose.

The refrigerant (mixture) is fed from the collection vessel to therefrigeration consumers via at least one liquid line. An expansiondevice, preferably an expansion valve, in which the refrigerant(mixture) flowing into the refrigeration consumer or the evaporator(s)of the refrigeration consumer is expanded, is connected upstream of eachrefrigeration consumer. The refrigerant (mixture) which has beenexpanded in this way is evaporated in the evaporators of the refrigerantconsumers and thereby cools the corresponding refrigeration cabinets orcold stores.

The evaporated refrigerant (mixture) is then fed via a suction line to acompressor unit. These compressor units may be of single-stage ormultistage design. The individual compressor stages generally have aplurality of compressors connected in parallel, which compress therefrigerant (mixture) and pass it back, via a riser, to the liquefierwhich has already been mentioned. Whereas the compressor unit isnormally positioned, for example, in a machine room arranged in thebasement of a supermarket, the liquefier is located on the roof of thesupermarket.

The compressors used are generally oil-lubricated reciprocating pistoncompressors which are driven in rotation. One drawback in this case isthat corresponding measures have to be taken to allow the oil releasedfrom the reciprocating piston compressor to be separated from therefrigerant (mixture). Furthermore, it is generally necessary to ensurethat the oil which has been separated off is fed back to thereciprocating piston compressor(s). To enable the oil to be separatedoff, the mixture of refrigerant and oil first of all has to be passed tospecific points within the cycle, and consequently minimum velocitieshave to be reached in rising suction and pressure lines, since the oilwould not otherwise be entrained. These minimum velocities mean smallpipe diameters, resulting in additional, undesired pressure losses andtherefore energy losses. To avoid these pressure and energy losses inrisers, it is necessary to split lines, but this in turn results inincreased installation outlay. Therefore, process aspects areundesirably closely linked to economic aspects.

As an alternative to the procedure described above, the system of a coldvapor refrigeration installation, in which a distinction is drawnbetween subcritical (with reliquefaction) and supercritical (with gasrecooling) operation, so that a “gas cooler” is used instead of the“liquefier” component, it is also possible for a gaseous refrigerant(mixture) to circulate in a refrigeration installation, which under thegiven boundary conditions (pressure, temperature, etc.) is not in liquidform at any time. This is then what is known as cold gas refrigerationinstallation, also referred to as a Joule, Stirling or Gifford-McMahoninstallation.

The text which follows will simply use the term “liquefier”. If theprocess in question is a cold vapor compression process in the two-phaserange, it is actually a liquefier that is used. In the case of asupercritical procedure or gas processes, the term “liquefier” in turnstands for a gas cooler. It is essential for heat to be dissipated fromthe cycle process. The liquefaction can take place in an air-cooledapparatus, in an intermediate-pressure separator or alternatively bymeans of a further assembly connected in a cascade. A cascade connectionis present whenever there is a further refrigeration machine which isoperated at a higher temperature level and which alone dissipates theheat of liquefaction to the environment. The refrigeration set is inthis case dependent on this refrigeration machine and in turn transfersits heat of liquefaction thereto. By way of example, it is possible fora standard cooling set to be connected upstream of a freezing set, inwhich case the two cooling sets may have different refrigerants orrefrigerant mixtures.

If what are known as normal cooling points and what are known asfreezing points are present inside a hypermarket or supermarket, theseare generally supplied by means of separate refrigerant cycles; thistherefore means that there are at least two refrigeration installationsas described in DE-C 39 28 430.

The refrigeration installation or the evaporators arranged in therefrigeration consumers have to be defrosted at regular intervals, sincefrosting or icing of the evaporators leads to a reduction in theefficiency of the evaporators. One defrosting option is electricaldefrosting, in which the evaporators are defrosted by means ofelectrical heaters arranged in and/or on them. However, this procedureleads to an undesirable increase in the consumption of electricalenergy.

What is known as compressed gas defrosting is a recommended alternativeto the electrical defrosting described above. In this case,compressed-gas lines are laid between the gas space of the collectionvessel connected downstream of the liquefier and each evaporator orevaporator module, and refrigerant, which is preferably at a temperatureof between 35 and 45° C., is fed from the collection vessel to theevaporators or evaporator modules via these compressed-gas lines.However, the installation outlay for this compressed-gas defrosting isrelatively high, since either a separate compressed-gas line has to beprovided for each evaporator or each evaporator module or, as iscustomary in the two-wire system, switching valves and a second setcomprising the same refrigerant (mixture) are required. Furthermore,there is the possibility of defrosting by means of circulated air attemperatures above approx. 2° C.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a refrigerationinstallation of the generic type which in terms of investment andoperating costs and also reliability has advantages over therefrigeration installations of the prior art.

To achieve this object, the invention proposes a refrigerationinstallation which is distinguished by the fact that

-   -   the expansion members are designed as modified expansion valves        and/or as modified linear expansion machines or are assigned        bypass lines, and    -   each refrigeration consumer is assigned a modified linear        compressor or a conventional compressor, which includes a bypass        line,    -   the modified expansion valve(s) and/or the modified linear        expansion machine(s) and/or the modified linear compressor(s)        having a working position which allows flow to pass through        without a significant pressure drop.

Most linear compressors operate as oil-free cryogenic Stirling coolersat extremely low temperatures and extremely low powers, i.e. incold-vapor compression. In cold-vapor compression, linear compressorshave only been implemented for a few years and have hitherto not beendeployed extensively. In the cooling sector, the applicant is only awareof one application, namely the use of a linear compressor in a domesticrefrigerator. A drawback of linear compressors is that their productioncosts have hitherto been well above those of reciprocating-pistoncompressors driven in rotation, but of a similar order of magnitude toinverter compressors. Only in the 1960s were efforts made to exploit theadvantages of linear compressors. The principle of friction-freemounting of the piston only dates from this time. Even so, it was onlyin the 1990s that improvements were made to the operational reliability,by virtue of reliable electronic reciprocating controllers. In thiscase, it was or is necessary in particular to ensure that for examplefluctuating pressures do not lead either to the piston striking thecylinder head or to premature termination of the reciprocating operationat the top dead center, associated with an excessive damage volume andvolumetric or energy drawbacks of re-expansion.

Linear compressors have the advantage of allowing continuously variablepower control, which is realized by reciprocating control. Furthermore,they can be operated without oil. Furthermore, the condensate which isinevitably formed during defrosting operation does not cause any damageto them. Furthermore, they are superior in energy terms tooil-lubricating reciprocating piston compressors which are driven inrotation.

Although they are operated without oil, the oil-lubricated compressorswhich are driven in rotation are superior in energy terms. This resultson the one hand from the efficient linear motor and on the other handfrom the elimination of the mechanical losses, of which about 80% occurat the driving mechanism and about 20% at the piston. The piston of alinear compressor is mounted without contact and can be guided by whatare known as flexible bearings, which allow axial mobility combined withradial rigidity. This ultimately means a spring combination of uncoilingand coiling springs which impart a rotary movement to the piston aboutits longitudinal axis in addition to its periodic translatory movement.

Since they do not have any sliding-contact bearings, linear compressorscan be operated without oil. This absence of oil gives rise to numerousadvantages. In the case of compressed-gas defrosting with condensation,the bearings, which have hitherto been relatively vulnerable, can nolonger be damaged by liquid refrigerant (mixture). The formation of acidwhich is known when using lubricating oils and can lead to burn-out ofthe winding of built-in motors, has hitherto been more or lesseffectively avoided by the use of refrigerant dryers. These molecularsieve dryers can now be dispensed with unless the water content is sohigh that there is a risk precipitation of ice during the expansion.Irrespective of this, it is recommended that dirt filters be providedimmediately upstream of the expansion valves or machines.

Linear compressors also have the advantage of not being damaged by thepumping of liquid, unlike other designs of compressor. The pumping ofliquid is of relevance in particular after the end of a defrostingprocess, since at this time under certain circumstances condensate maystill be present in the defrosted evaporators, and this condensate issucked in by the compressor when it starts to operate again. However, itshould expediently be ensured that liquid is pumped carefully. Thismeans beginning with small reciprocating strokes, in order to limit themaximum power of the compressor during the conveying of liquid and toprotect the working valves and reciprocating movement dampers. A designsolution in which a disk valve as pressure valve replaces the cylinderhead has also already been proposed; this leads to very high operationalreliability.

Unlike the known refrigeration installations from the prior art, it isnow possible to implement circuits in which the feed and discharge linesassigned to the refrigeration compressor(s) contain the liquid that isto be injected as well as the compressed gas of the compressor(s).Therefore, on the one hand there is no need for a central suction line,and on the other hand the compressors are no longer spatially separatefrom the consumer(s), but rather are located in the immediate vicinityof the refrigeration consumer(s).

The compressor sets which it has hitherto been necessary to provide inrefrigeration installations can now be dispensed with, since eachconsumer is assigned at least one dedicated compressor. Therefore, eachconsumer can be controlled individually and, moreover, continuously bymeans of its own compressor. Unlike in the known procedures orrefrigeration installations, this individual control can now take placeirrespective of the temperature level in the return line, since thereturn or discharge line now no longer represents the suction line, thepressure of which is dependent on the evaporation temperature, whichpredetermines the temperature of the refrigeration consumers, but ratherrepresents the pressure line.

If this is not impossible on account of other boundary conditions, it ispossible, for example, for freezer cabinets to be temporarily used andoperated as standard refrigerator cabinets and/or display shelves forfresh meat and at times for dairy products. In the simplest case, thischangeover is effected by adjusting a temperature selection button onthe refrigeration cabinet in question. Furthermore, a pressure line hasa smaller diameter compared to the corresponding suction line andmoreover does not require any insulation.

As has already been mentioned in the introduction, the invention alsorelates to two alternative methods for operating a refrigerationinstallation of the generic type in order to realize a compressed-gasdefrosting method.

In this context, the first alternative of the method according to theinvention for operating a refrigeration installation is distinguished bythe fact that during the defrosting phase of the refrigeration consumeror at least one of the refrigeration consumers, the modified expansionvalve(s) and the modified linear compressor(s) of the refrigerationconsumer(s) which is/are to be defrosted is/are moved into the workingposition in which through-flow without a significant pressure drop ispossible.

The second alternative of the method according to the invention foroperating a refrigeration installation is characterized in that duringthe defrosting phase of the refrigeration consumer or at least one ofthe refrigeration consumers, the associated bypass lines are opened andthe associated conventional expansion valve(s) and the associatedconventional compressor(s) are taken out of operation.

The refrigeration installation according to the invention, the methodsaccording to the invention for operating a refrigeration installationand further configurations of the refrigeration installation accordingto the invention and of the methods according to the invention will beexplained in more detail on the basis of the exemplary embodimentsillustrated in FIGS. 1, 2 and 3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a refrigeration installation;

FIG. 2 shows an alternative embodiment of a refrigeration installation;and

FIG. 3 shows another embodiment of a refrigeration installation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a refrigeration installation according to the invention,which is used to supply three refrigeration consumers V′, V″ and V′″. Ofcourse, there may be any desired number of refrigeration consumers. Therefrigerant or refrigerant mixture—referred to below simply as“refrigerant”—is fed to the above-mentioned refrigeration consumers viaa (central) feed line 1 and lines 1′, 1″ and 1′″ which branch off fromthis feed line 1.

According to the invention, either a modified expansion valve a, b or cis connected upstream of the evaporator of each refrigeration consumerV′, V″ and V′″ or

as illustrated in FIG. 2—the upstream conventional expansion valve a′has a bypass line 4, represented by dashed lines. FIG. 2 shows, on thebasis of the refrigeration consumer V′, by way of example, analternative configuration of the refrigeration installation according tothe invention to the embodiment illustrated in FIG. 1. As an alternativeto the modified expansion valves a, b and c illustrated in FIG. 1, it isalso possible to use modified linear expansion machines.

After expansion has taken place in the valves a, b and c or a′ describedabove, the expanded refrigerant is fed via the lines 2′, 2″ and 2′″ tothe evaporators of the refrigeration consumers V′, V″ and V′″, in whichit is evaporated.

The evaporated refrigerant is then fed back to the (central) return line3 via the return lines 3′, 3″ and 3′″ by means of the modified linearcompressors x, y and z. Instead of the modified linear compressors x, yand z illustrated in FIG. 1, it is also possible to provide aconventional compressor x′ which has a bypass line 5, illustrated bydashed lines; this embodiment of the refrigeration installationaccording to the invention is also illustrated in FIG. 2.

If the refrigeration consumer V′ or its evaporator, for example, is tobe defrosted, the modified linear compressor x and the modifiedexpansion valve a are moved into the working position in which flowthrough the modified linear compressor x and the modified expansionvalve a is possible without a significant pressure loss in therefrigerant. According to the invention, the warm refrigerant now passesout of the refrigeration consumers V″ and/or V′″, via the line 3′,through the opened, modified linear compressor x to the evaporator ofthe refrigeration consumer V′ and defrosts the latter. The refrigerantwhich has been cooled and possibly condensed as a result of thedefrosting process is fed back to the (central) feed line 1 via the line2′, the opened modified expansion valve a and the line 1′, and thenpasses back to the refrigeration consumers V″ and V′″ via the lines 1″and 1′″.

If—as illustrated in FIG. 2—bypass lines 4 and 5 are provided, theconventional expansion valve a′ and the conventional compressor x′ aretaken out of operation and the refrigerant required to defrost theevaporator of the refrigeration consumer V′ passes via the lines 3′ and5 to the evaporator of the refrigeration consumer V′ that is to bedefrosted. After defrosting has taken place, the refrigerant is then fedback to the (central) feed line 1 via the lines 2′, 4 and 1′.

According to an advantageous configuration of the refrigerationinstallation according to the invention, the refrigeration consumers V′,V″ and/or V′″ can—as illustrated in FIG. 1—be connected to the feed line1 and the discharge line 3 by means of couplings, preferably by means ofquick-acting couplings K, in particular by means of standardizedquick-acting couplings.

In addition or as an alternative to the procedure illustrated in FIG. 1,the refrigeration consumers V′, V″, V′″, . . . may also—as illustratedin FIG. 2—be connected to one another in segments and directly,including the main lines 1 and 3. In this context, it should be ensuredthat under certain circumstances consumers or liquefiers at a differentlevel—i.e. for example cold stores which are arranged on differentfloors of a hypermarket—are connected to one another, although in thiscase direct coupling or connection is not possible.

The flexibility of the refrigeration installation according to theinvention can be increased further by means of these above-describedadvantageous configurations of the refrigeration installation accordingto the invention.

Both methods according to the invention for operating a refrigerationinstallation now make it possible for one or more refrigerationconsumers that are to be defrosted simultaneously to be defrosted by theother refrigeration consumer(s) which are in the cooling phase. This isdone without the need for additional pipe networks and/or additionalenergy sources, as were required hitherto for compressed-gas defrosting.

As a refinement to the refrigeration installation according to theinvention, it is proposed that

-   -   the refrigeration consumer or at least one of the refrigeration        consumers has a dedicated closed refrigerant (mixture) cycle,    -   the refrigerant (mixture) cycle(s) is/are operatively connected        via at least one liquefier to the feed line and the discharge        line, and    -   the refrigerant (mixture) cycle(s) in each case has/have        modified expansion valves and/or modified linear expansion        machines or conventional valves with associated bypass lines and        modified linear compressors or conventional compressors with        associated bypass lines,    -   the evaporator of a refrigeration consumer in each case being        arranged higher than the liquefier of the refrigeration        consumer.

FIG. 3 shows by way of example with reference to refrigeration consumerV′ the above-mentioned configuration of the refrigeration installationaccording to the invention.

In this case, the refrigeration consumer V′, V″ or V′″ as a dedicatedrefrigerant (mixture) cycle 6, 7, 8 and 9, which is operativelyconnected via the liquefier E to the feed line 1 and the discharge line3. The refrigerant (mixture) cycle 6, 7, 8 and 9 has either a modifiedexpansion valve a and a modified linear compressor x or a modifiedlinear expansion machine, or else the conventional valve and/or theconventional expansion machine and the conventional compressor areassigned bypass lines, which are indicated by dashed lines in FIG. 3.

Those line portions and components which form part of the refrigerationconsumer itself are surrounded in FIG. 3 by the dot-dashed line. Thismay optionally include the feed line 1 and discharge line 3.

In order now in defrosting operation to allow an automatic refrigerant(mixture) recirculation to be realized, it is necessary for theevaporator of the refrigeration consumer V′ to be arranged at a higherlevel than the heat exchanger E.

This configuration allows the flexibility of the refrigerationinstallation according to the invention to be increased significantlycompared to refrigeration installations of the generic type, since thisconfiguration of the refrigeration installation according to theinvention allows the (retrospective) inclusion of further refrigerationconsumers in the refrigeration installation assembly.

As has already been mentioned, in the refrigeration installations of theprior art, it is always necessary to provide at least two separaterefrigerant (mixture) cycles if both normal cooling and freezing pointsor consumers are to be supplied with refrigeration. This problem islikewise eliminated by the refrigeration installation according to theinvention, since now only one refrigerant (mixture) cycle needs to beprovided.

The linear compressors that are to be provided are operated without oil.Therefore, the refrigeration installation according to the inventioneliminates all the measures which have hitherto been required toseparate off, recirculate, distribute and store the oil. Sincetransporting and distributing the oil within the pipe network is nolonger of relevance, the individual lines or line sections can now bedimensioned exclusively on the basis of economic criteria.

The invention means that it is now no longer necessary to install whatare known as combined refrigeration sets. Rather—at least in arelatively large area—it is possible for a large number of individualand if appropriate different refrigeration consumers to be linked intoor removed from an existing system comprising liquid line, gas orpressure line and liquefier, if appropriate retrospectively. This ismade possible in particular by virtue of the fact that it is possible todispense with the above-described compressor sets of the combinedrefrigeration installations that have hitherto been required, since eachrefrigeration consumer now has its own compressor, which is adapted tothe prevailing boundary conditions and specifics of the refrigerationconsumer.

1-6. (canceled)
 7. A refrigeration installation having at least onerefrigeration consumer, which includes at least one evaporator, havingat least one feed line and at least one discharge line, via which arefrigerant or a refrigerant mixture is fed to the at least onerefrigeration consumer and discharged from the at least onerefrigeration consumer, the at least one evaporator having expansionmembers, wherein the expansion members being designed as modifiedexpansion valves and/or as modified linear expansion machines or beingassigned bypass lines, and each said refrigeration consumer beingassigned a modified linear compressor or a conventional compressor,which includes a bypass line, and the modified expansion valves and/orthe modified linear expansion machines and/or the modified linearcompressors having a working position which allows flow to pass throughwithout a significant pressure drop.
 8. The refrigeration installationas claimed in claim 7, wherein the at least one refrigeration consumerhas a dedicated closed refrigerant or refrigerant mixture cycle, therefrigerant or refrigerant mixture cycle being operatively connected viaat least one liquifier to the at least one feed line and the at leastone discharge line, and the refrigerant or refrigerant mixture cycle ineach case having modified expansion valves and/or modified linearexpansion machines or conventional valves with associated bypass linesand modified linear compressors or conventional compressors withassociated bypass lines, the evaporator of said at least onerefrigeration consumer in each case being arranged higher than theliquifier of the said at least one refrigeration consumer.
 9. Therefrigeration installation as claimed in claim 7, wherein a plurality ofrefrigeration consumers are connected to one another and/or to the atleast one feed line and the at least one discharge line by means ofcouplings.
 10. The refrigeration installation as claimed in claim 9,wherein said couplings are quick-fit couplings.
 11. The refrigerationinstallation as claimed in claim 7, wherein said at least one of therefrigeration consumers is assigned supercoolers as internal heatexchangers.
 12. A method for operating the refrigeration installation asclaimed in claim 7, comprising assigning at least one refrigerationconsumer modified expansion valves and modified linear compressors, andduring the defrosting phase of at least one of the refrigerationconsumers moving at least one of the modified expansion valves and atleast one of the modified linear compressors of the refrigerationconsumers which are to be defrosted into a working position in whichthrough-flow without a significant pressure drop is possible.
 13. Amethod for operating a refrigeration installation as claimed in claim 7,comprising assigning at least one conventional expansion valve and atleast one conventional compressor of the at least one refrigerationconsumer bypass lines, and during a defrosting phase of the at least onerefrigeration consumer, opening the bypass lines, and taking the atleast one associated conventional expansion valve and the at least oneassociated conventional compressor out of operation.